Apparatus for and method of separating gases



Jan. 26, 1954 s. c. COLLINS APPARATUS FOR AND METHOD OF SEPARATING GASES 2 Sheets-Sheet l Filed Feb. 9, 1951 Jan. 26, 1954 s'. COLLINS 2,657,044

APPARATUS FOR AND METHOD OF' SEPARATING GASES Filed Feb. 9, 1951 2 Sheets-Sheet 2 Patented Jan. 26, 1954 APPARATUS FOR AND METHOD F SEPARATING GASES Samuel C. Collins, Watertown, Mass., assigner to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Application February 9, 1951, Serial No. 210,147

22 Claims. (Cl. 62123) This invention relates to the separation of gases into their constituents, especially to the separation of air into oxygen and nitrogen.

The separation of air into its components is quite readily accomplished at low temperatures by taking advantage of the different boiling points of oxygen and nitrogen. This method of separation of course requires refrigeration, and it is common practice to utilize the low temperature of the products-the separated oxygen and nitrogen-to cool the incoming air. This method is based on a nice balance between oooling required by inilowing air and refrigeration available in the cold products, with losses made.

up by added refrigeration provided by expanding some of the air in doing external work. -Under certain circumstances, it ls desirable to produce oxygen in the liquid form. When oxygen is taken out as liquid, there is-necessarily a substantial refrigeration loss which must be made up in some manner.

It is an object of this invention to provide an apparatus and method for the production of oxygen, preferably in the liquid form. This and other objects are accomplished in an apparatus and method in which a primary circuit comprises the main air circuit, the product oxygen, and the eiuent waste gases, and a secondary circuit comprises a refrigeration circuit, preferably nitrogen gas being circulated as a refrigerant.

In the drawings:

Fig. 1 is a diagram showing apparatus for accomplishing the purpose set forth above, in which the secondary circuit shows a threestage expansion engine: sind Fig. 2 is another embodiment of the invention in which the secondary circuit employs a singlestage expansion engine, and in which the oxygen product may be taken out as liquid or in the alternative as gas.

In the embodiment shown in Fig. l, an air inlet 2 is shown as a conduit connected to the intake of an air compressor 4. The compressor 4.

is preferably a two-stage compressor having a low pressure stage Ii. a high pressure stage B, an intercooler I0, an aftercooler I2. and appropriate connecting conduits, as will be understood by those skilled in the art. The compressor 4 thus comprises a source of air under pressure.

A reversing valve is shown at I4 connected with the source of air under pressure by first-named conduit means I8. .A reversing heat exchanger is provided as indicated generally at I 8. The invention preferably comprises at least e reto divide the heat exchanger I8 into three small heat exchangers 20, 22 and 24 in order to keep the height of the unit to a minimum. Reversing heat exchanger I8 is connected with the reverslng valve I4 by second-named conduit means 28. Where the heat exchanger Ill is broken down into three separate units, similar fluid passages in units 20, 22 and 24 are connected together by means of conduits 23 and 30, the conduits 28 and 30 forming with said passages and with the conduit 26 one continuous Ailulci passage;

A second reversing valve 32 is shown connected with the heat exchanger il 8 by third-named conduit means- 34t The 'reversing valve 32 may if desired be similar tothe reversing valve I4 and be mechanically operatedgir? the valve 32 may in the alternative be a reversing check valve. as shown dlagrammatlcallyln A reversing check valve such 'as is in Fig. 1 may be provided with chambers 36:18, 48, and 42. chambers 38-40, 38-442, Il-36, and 42-36 being provided with suitable interconnecting openings, Check valves 43, 44546, and 48 are provided to engage suitable seats surrounding the aforesaid openings, asv will be well understood by those skilled in the art.

A rectication column 50 is shown, the column being preferably of the double-columntype provided with suitable packing which may be any rather porous substance such as stainless steel `or brass fine mesh screen in the shape of saddles or any other suitable shape. As in the case of the heat exchanger I 8. the column 5t may be made of a smaller height by making the upper portion of the upper column in two parts. Thus. as here shown. the upper column is provided in two sections E2 and 5 The rectincation column has an air inlet 54, an oxygen product outlet 53.*,a nitrogen eilluent outlet 58, secondary circuit inlet and outlet connections 60 and B2 respectively. and other connections which will be described below. Means are provided to connect-the second reversing valve 32 with the air inlet 54. These means include fourthnamedV conduit means 64, which might be connected directly 4with the second reversing valve 32, Ibut in the preferred form will include other elements as will be described below.

Means are also provided to connect one of the product outlets with the second reversing valve: in the embodiment shown in Fig. 1 this means includes fifth-named conduit means 66 connecting. directly with the nitrogen eiilueut outlet 58: conduit G6 might connect directly with the reversing heat exchanger, but it may be desirable verslng valve 32, but in the preferred form of the invention connects with valve 32 by Way ot additional means as will' be described in greater detail below. Sixth-named conduit means 68 are provided to connect the second reversing valve 32 with another passage in heat exchanger IB.

As was indicated above. in the embodiment shown the heat exchanger I8 is broken down into three separate units 20. 22 and 24: the sixthnamed conduit means EB referred to above connects with one end o! one of the passages in unit 24. and a conduit 10 connects the other end of that passage oi' unit 24 with a similar passage in unit 22: the other end of that passage in unit 22 com'- municates by way of a conduit 12 with one end oi a similar passage in unit 20, and the other end of that passage connects by way of seventh-named conduit means 'i4 with the mst-named reversing valve It. Reversing valve i4 is'prov'ided with a waste gas efiiuent (or nitrogen product) outlet 16. Returning now to the rectication column, indicated generally by the reference character 80, the oxygen-rich liquid air outlet at the bottom of the lower column is connected by a conduit i8 with a liquid inlet 80 in the upper column section temperaturkes encountered-gases in the uppeil portion oi he boiler-condenser in the middle oi the column. Without such a bleed uncondensable gases are likely to accumulate and render the column inoperative. Bleed line 96 may be of such small conduit as to 'limit iluid ilow therethrough to .the very small percentage required, to avoid wasting gas, or il desired, a variable restriction, not shown, may be provided in the bleed line.

Liquid oxygen product is taken from the boilercondenser in the middle o! the column by way of an outlet 88 connecting through a valve |00 with an outlet conduit |02. Outlet conduit |02 connects with a subcooler |04 having a liquid oxygen passage therethrough. the other end of which connects with a conduit |06 which receives liquid oxygen from any suitable liquidpump |08; the pulnp in turn is connected with the product outlet 56 by a conduit H0. The subcooler has another passage through it and connects with the waste gas eilluent line 6B and is an additional means (additional to the fifth-named conduit means EB referred to above) connecting the nitrogen product outlet 58 with the second reversing valve 32.

52'. As will be well understood by those skilled 251 The subcooler |04 serves to cool the liquid in the art, the inlet 80 is provided at that point in the column section where the equilibrium opera'ting condition provides down-flowing liquid ot substantially the same composition as the ingoing oxygen-rich liquid air. 4The conduit 'I8 is provided with an expansion valve 82.. y

Liquid collecting in the bottomot the ,upper column section 52' is pumped to the top of the upper column portion 52 by way of anysuitable liquid pump 0l and connecting conduits B6 and B8. It will of course be understoodfby those sinned in the art that, where there are no height limitations imposed upon the apparatus (seeqthe description of Fig. 2 below). the upper column section 52 may it desired'be stacked immediately on top of the upper column section 52, in which case liquid trickling, downward through 'the column will simply fall th'e entire length of the upper column and there will then be no need for the connecting conduits B6 and 88 and the liquid pump Bl.

an apparatus will not require the section 52' is stacked immediately on top of the column section 62, so that the vapor redux or gaseous eilluent may ilow directly from the upper end oi' the column section 52 into the column section B2. As a matter o! fact, there will be no .dividing boundary or partition between the sections 52 and 52'. but there will be instead one continuous upper column section (as in Fig. 2, de-

scribed below).

Nitrogen-rich liquid collecting in the nitrogen section may be trama shelf o! the lower column fen-ed therefrom to the upper end ot the upper column section S2' by a suitable conduit 92. A restriction such as the expansion valve 94 is provided in the conduit as will be understood by those skilled in the art.

A rare gas bleed 06 connects the upper portion of the boiler-condenser in the middle of the double-column with the waste gas or nitrogen eiliuent line 66. It will be understood by th skilled in the art that a bleed such as the conduit 96 shown is provided toprevent the accumulation nf uncondensahle--i. e., at the normal operating oxygen product below its boiling point at storage pressure suinciently to prevent excessive loss of liquid upon the emptying of such oxygen from the column through the valve I 00 to such storage facilities as may be provided.

Reference will now be made to the secondary or refrigeration circuit of this apparatus. In this circuit there is Va nitrogen compressor indicated generally at 2. which is preferably a two-stage compressor having a low pressure stage H4, a high pressure stage IIB, an intercooler H8. and an attercooler |20. Compressor ||2 has the usual inlet and discharge connections |22 and |24, respectively.

There is a second-named heat exchanger which. again, may i! desired be in a single unit. but which in the embodiment show in Fig. l consists of a plurality of units. One such unit is that shown at |25, which has a passage connecting with the discharge connection i2( by nist-named secondary circuit conduit means |21. Another unit of the second-named heat exchanger is shown generally at |28 and consists oi sections |30, |32 and |34.

' Units |26 and |28 are interconnected by suitable conduits as will be explained in detail below,

An expansion engine |36 is provided in the secondary circuit. This expansion engine may if desired be s. single cylinder engine, but in the preferred form. comprises a three-stage expansion engine having cylinders |38, |00 and |42. As used here, "three-stage means that the expansion takes place at three diierent temperature levels. The expansion engine stages are preferably provided with any suitable surge capacity indicated at IM, and |48. Each stage of the expansion engine is of course provided with intake and exhaust ports. For the purpose of this description, it will be assumed that the intakes to the surge capacities constitute the intakes for the expansion engine cylinders. Thus, the stages |38, |40 and |42 have intake ports |50l |52 and respectively, and exhaust ports I 56, |58 and A single-stage expansion engine would have its intake port connected with the second-named heat exchanger by a single simple conduit. In the embodiment shown in Fig. 1, the stage |38 having the intake port is connected with the second-named heat exchanger by means which include second-named secondary circuit connects with a second reversing valve 332 by third-named conduit means 334.

'I'he reversing valve 332 shown in Fig. 2 is substantially identical with the reversing valve 32 shown in Fig. l, both of these valves being shown as reversing check valves; however. if desired, reversing valve 332 may be identical with reversing valve 3|4, and mechanically connected to operate at the same time that valve 3|4 is operated.

A rectification column 350 is provided. this column preferably being of the double-column type somewhat similar to the column shown at 50 in the embodiment of Fig. l. except that the upper column 352 (Fig. 2) is shown in a single section integral with the lower column, because it is assumed that the embodiment shown in Fig. 2 does not have the height limitations which are imposed on the embodiment shown in Fig. 1.

Rectilication column 350 has an air inlet 354, an oxygen product outlet 35B, a nitrogen eilluent outlet 358, secondary circuit inlet and outlet connections 3E!! and 362 respectively. and other connections which will be described below. Means are provided to connect the second reversing valve 332 with the air inlet 354. These means include fourth-named conduit means 364, which may if desired be connected directly with the second reversing valve 332, but in the preferred form will include other elements as will be described below.

Means are also provided to connect one oi the product outlets with the second reversing valve; in the embodiment shown in Fig. 2, this means includes mth-named conduit means 36E connecting directly with the nitrogen eluent outlet 358; conduit 36 may if desired connect directly with the reversing valve 332, but in the preferred form of the invention, connects with valve 332 by way of additional means as will be described in greater detail below. Sixth-named conduit means 368 are provided to connect the second reversing valve 332 with another passage 389 in heat exchanger SIB. The other end of passage 359 is connected with seventh-named conduit means 314, which connects with the reversing valve 3H. Reversing valve 314 is provided with a waste gas effluent (or nitrogen product) outlet 316.

Returning now to the rectiiication column indicated generally by the reference character 358, the oxygen-rich liquid air outlet at the bottom of the lower column is connected by a conduit 318 with a liquid inlet 280 in the upper column 352. The conduit 318 may if desired pass through a heat exchanger 38|. and includes a. restriction such as the expansion valve 332. Nitrogen-rich liquid collecting in the nitrogen shelf of the lower column may be transferred theretrom..to. the upper column by a suitable conduit 392, this conduit preferably passing through the heat exchanger 88i. A restriction such as the expansion valve 394 is provided in the conduit for reasons that will be understood by those skilled inthe art. x

As in the embodiment shown in Fig. l. a rare gas bleed 39E is preferably provided from the upper portion of the boiler-condenser in the middle of the double column, the bleed connectlng with the waste gas or nitrogen eiiiuent line 366.

The product oxygen outlet 355 is preferably provided in the form of o. tap into the liquid collecting pot or boiler-condenser in the middle or the column. Where the oxygen product is desired in the liquid state. it may be removed through a tap or outlet 398 connecting through a valve 400 with an outlet conduit 402. Outlet conduit 402 connects with the liquid oxygen outlet 356 by a connecting conduit 464. When it is desired to remove oxygen from the column in the vapor state. that is accomplished through an outlet 406, that outlet being in the form oi a substantially vertical stack portion which allows droplets to fall out of the vapor stream back into the column.

Reference will now be made to the secondary or refrigeration circuit of the apparatus shown in Fig. 2. In this circuit there is a nitrogen compressor 4I2 which may if desired be driven from the same source of power as the air compressor 384. Compressor 4 I 2 has the usual inlet and discharge connections 422 and 424 respectively.

There is a second-named heat exchanger ,428 which, in the embodiment shown in Fig. l, was shown as consisting of a plurality of units, but which in the embodiment shown in Fig. 2 now being described preferably consists of a single unit as shown. First-named secondary circuit conduit means 429 connects the discharge 424 of compressor 412 with a passage 43| in heat exchanger 42S.

An expansion engine 436 is provided in the secondary circuit. This expansion engine is desirably a single cylinder engine having intake and discharge ports 450 and 458 respectively. Intake port 458 is connected with passage 43| of the second-named heat exchanger 423, by second-named secondary circuit-conduit means 462. A. liquefier 464 is provided; a passage 461 thereof is .also connected with passage 431 of the second-named heat exchanger'-428 by lthirdnamed secondary circuit conduit means 466, and a portion of the conduit means 462.` A liquid conduit -418 is connected with the other end of passage 461 in liqueer 464 and with the aforesaid secondary circuit column inlet connection 368. A combined shutoiland expansion valve 41| is preferably providedfln the4 line 410.A

Means are provided to connect the expansion engine exhaust port 455 with the compressor inlet connection 422. those means including the liquefier 464 end heat exchangers 3i8 and 428. Fourth-named secondary circuit conduit means 412 are provided to connect the secondary circuit column outlet connection 862`with the last-named means. ,l i

Referring tog-the "last-named means" in greater detail, a conduit 416 connects with the expension engine exhaust gas outlet 456 at its one end and at its other end connects with a passage 411 in the cold end of reversing heat exchanger BIB. Conduit 416 is provided with a branch 418 connecting with one end of a passage 419 in liquetler 464: the other end of passage 419 connects by way of a conduit 480 with the secondnamed heat exchanger 428. Variable restrictions 48i and 482 in the conduits 480 and 418 respectively are preferably provided to enable balancing of the iluid flows in the two lines at the desired ratio.

A check valve 463`is preferably provided in the conduit 416 to permit duid ow only in the direction from the expansion engine toward heatl exchanger 428. A conduit 484 having a normally closed shutoi valve 486 connects the nitrogen eilluent line 386 with the conduit 416. The fourth-named secondary circuit conduit means 412 referred to above connects with conduit 416 at 492. Conduit 416 was referred to above as connecting at one end with a passage 411 in heat exchanger 3| 8. The other end of passage 411 connects by way of a conduit 496 with a passage 428 in heat exchanger 42E. Passage $6 extends substantially throughout the length of heat exchanger 32.7 and is connected at its one end with the conduit 430. and at its other end with a conduit 502 which connects with the inlet 422 of the nitrogen compressor.

Reference is made above to the means to conneet product outlet 356 with the second reversing valve 32-2, those means including the ifthnamed conduit means 356. Those means also include a passage 505 in liquener 464, one end of which is connected with the eiliuent line 356 and the other end of which is connected with a conduit 507. reversing check valve 332.

The foregoing description referred to the desirability at times to remove oxygen product in the vapor state. Vizen gaseous oxygen is desired. it is possible to utilize the refrigeration present in the cold oxygen product. This may be accomplished in the manner shown in Fig. 2. whereby a conduit 569 is connected to the upper end of the stack portion 406. and connects with a passage 5|! in liqueer 464. A conduit 5|'3 connects the other end of passage 5H with a passage 5| 5 in heat exchanger 3|8. connection 5I? connects with the passage SI5 and may conduct the gaseous oxygen to any desred oxygen utilizer. for example a booster pump which raises the pressure of the gaseous oxygen to a high value for the purpose of storing the oxygen in bottles, or to some lesser pressure direct to a shop line.

The above description indicates that fourthnamed conduit means 364 forms one of the elements of the means to connect reversing valve 332 with air inlet 354. Another element is passage 5| 9 in liqueer 484, one end of which connects with conduit 364 and the other end of which connects with still another element, conduit 530. which in turn connects with valve 332.

Operation Reference isnow made to the operation of the embodiment of the invention shown in Fig. 1.

In the discussion of the operation of this emto cool down or start the apparatus will be des:

scribed.

Compressed air at approximately 80 p. s. i. g. and 110 F. is supplied by the air compressor 4. passing through conduit i6, reversing valve I 4. and conduit 26, to the reversing heat exchanger i8. The air passes through a passage in unit 20, from thence to unit 22 by way of conduit 2B, through a passage in unit 22, from there to a passage in unit 24 by Way of conduit 30, and leaves the reversing heat exchanger I8 by way of conduit 34.

Conduit 34 conducts air to the reversing check valve 32. namely to chamber 40 of valve 32. The compressed air lifts valve 43 offits seat, and thus ilows into chamber 36 and out through conduit 230 to the heat exchanger 226. Air enters heat exchanger 226 at 262 F. andat 87 p. s. i. g. Air leaves the heat exchanger 226 by way of the conduit 64 and enters the lower column by way of the air inlet 54, at 275 F. and at 87 p, s,

An outlet Conduit 581 is connected `with thenamed heat exchanger.

i. g.. and approximately 6% of the air by weight is liquid.

The eilluent gases, mostly nitrogen, leaving the column by way of conduit 66 are at approximately 7 p. s. i. g. and at 314 F. The eilluent gases pass through subcooler |04 and heat exchangers 226 and IB ln turn. giving up their refrigeration and absorbing heat from the incoming air. The eiiiuent gases leave heat exchanger 226 and enter heat exchanger IB at 269 F. and 6 p. s. i. g., and leave the connection 16 at approximately 104 F. and atmospheric pressure.

Liquid oxygen product leaves the column by way of conduit |I0 at a'temperature of 290 F. and a pressure oi 7 p. s. i. g., and passes through the subcooler |04-to storage under pressure, corning out of the subcooler at approximately 298 F. and p. s. l. g. With liquid oxygen product outlet 56.located at the normal liquid level, product oxygen leaves the column, in the liquid form. as liquid tends to build up above the normal level. Thus, product oxygen overflows through the conduit ||0 and is pumped to storage through the aforesaid path.

Referring now to` the secondary circuit, compressed nitrogen leaves the nitrogen compressor ||2 by way of conduit |2| at approximately 450 p. s. i. g. and,approximately..110 F.` This nitrogen passes to the unit |26of the second heat exchangerfand leaves unit |26 by way of conduit 200 at approximatelyiSO p.fs. i. g. and 44 F. A portion (approximately 14.8%) ot the nitrogen is takenfrom conduit 208 by way of conduit 2 i2 to the iirst-stagexlcylinder |42 of the expansion enginellE. This-prtion-.is expanded isentropically to a pressure of approximately 84; p. s. i. g. and a temperature of' 270 F., leaving the nrst stage by way otconduit 2 I4 :and going to passage 2|6 in section |30 of the unit I 2B ofthe second- In section |30, passage 2|6 joins passage |98, and the gases pass by way oi' conduit 200 at 32 F. and 82 p. s. i. g. to the unit |26. leaving the unit |26 at 81 p. s. i. g. and 103 F.

Reference was made to a portion (14.8%) of the nitrogen being taken from conduit 208 by way of branch conduit 2|2. 'Ihe remainder (85.2%) of the gas in conduit 208 passes to the section |34, namely passage 2|0 in section |34, and this portion is again divided. Some (29.8%) of the remaining nitrogen is taken from the passage 2|0 by way of passage 2|8 and conduit 22d at 73 F. and 450 p. s. i. g. This portion is expanded isentropically to 85 p. s. i. g. in the second stage of the expansion engine |36. and leaves the second stage at 168 F. by way of conduit 222, passing to unit |28. More specically, conduit 222 connects with passage 224 in section |32, and passage 224 connects with passage |98.

Reference is made to the above discussion of the passage 2 I0 and the branch 2 i8 which takes some 29.8% of the nitrogen from passage 2|0. The remainder (about r10.2%) o'i' the nitrogen "from passage 2|0 leaves the unit |28 by way of conduit |66 at 199 F. and'450 p. s. i. g. A portion thereof is tapped od by way of conduit |62 for the third stage of isentropic expansion in cylinder |00 of expansion engine |36. Here the nitrogen expands from approximately 450 p. s. i. g. and 199 F. to 8'?, p. s. i. g. and 280 F.

The exhaust from cylinder |38 passes to liquener |64 by way of conduits |16 and |10. being joined in |18 by a portion of the gas from connection 62. The .exhaust from stage |38 is at 280 F. and 87 p. s. i. g. Gas from connection 62 and flowing downward in conduit |16 is at 282 F. and 87 p. s. i. g. They mix in conduit |18 and enter the liqueiier at` close to 280 F. (over 96.9% of the gas in conduit |18 comes from cylinder |38) and at 8'1 p. s. i. g. The resultant mixture enters liquefier |84 from conduit |18 and gives up its refrigeration to the remaining nitrogen from conduit |66 which enters the liqueiler as a gas at approximately 199 F. and 450 p. s. i. g. and leaves the liquetier as liquid at 271' F. Nitrogen gas leaves liquefier |64 by way of conduit |80 at 238 F. and 85 p. s. i. g., and ows to passage |98 in unit |28 of the second-named heat exchanger.

Reference is made again to connection 62 and the fact that a portion (18%) of the gas in connection 62 is tapped ofi for liqueier |64. going by way of conduits |16 and |18. The remainder of the gas in connection 62 passes to tlie unit 24 of heat exchanger IB, at 282 F. and 87 p. s. i. g. In unit 24, the gas gives up its refrigeration to supply part of the refrigeration which is lost by the removal of liquid oxygen. Secondary circuit nitrogen gaa leaves unit 24 by way of two conduits |94 and |86. Conduit |96 connects with passage |98, and secondary circuit nitrogen leaves unit 24 of heat exchanger I8 at 165 F. and 86 p. s. l. g. The remainder (82 3%) of the gas from unit 24 passes to units 22 and 20 by way oi' conduits |94 and 204 respectively, leaving the unit 20 by wav of conduit 206 at 103 F. and 8l p. s. i. g. Conduit 206 joins conduit 202 at 201.

Liquid nitrogen from liqueiier |64 leaves by conduit |10 at 271 F. and 450 p. s. i. g., and undergoes substantially isenthalpic expansion in expansion valve I1I, entering the column as a mixture of gas and liquid by way of the secondary circuit inlet connection 60 at 282 F. and 8'? p. s. i. g. The liquid nitrogen thus put into the column supplies additional refrigeration for the column. An equal quantity of gaseous nitro- Een leaves the column as aforesaid at 282 F. and 87 p. s. i. g. by way of secondary circuit column outlet connection 62, check valve |14, and conduit |12.

As raw air passes through the conduit 26 and the appropriate passages in units 20, 22 and 24 of heat exchanger I8. it is cooled by nitrogen from the column passing through other passages in units 24, 22 and 20, leaving heat exchanger I8 by way ci' conduit 14. After a time lapse of approximately two and one-half minutes, valve |4 is reversed. This reversal may be accomplished in any desired way, as for example by a cam connected to be driven by the compressor motor. Reversal of valve |4 as shown diagrammatically merely constitutes turning the valve through 90". Entering raw air thereupon switches from the conduit 26 to the conduit 14, and ci course enters the system by way of the passages which have just been used by the outgoing nitrogen. Conversely, the outgoing nitrogen passes outward through heat exchanger I8 in the passages which have just been used by the iniowing air.

The inflowing air during its passage through conduit 28 and the connected passages in heat exchanger I8 leaves its water and carbon dioxide in the form of deposits in the heat exchanger |8. Those impurities are carried out by the eilluent nitrogen during the next part of the cycle in which the eiiluent nitrogen is in the passages which were just occupied by inflowing air. Thus, the raw air deposits its water, carbon dioxide, and other impurities in certain passages posits of impurities which of heat exchanger I8 during one portion of the cycle which lasts about .two and one-half mlnutes, after which the air and nitrogen passages are interchanged, and during the next portion of the cycle lasting also approximately two and one-halt minutes, the nitrogen sweeps out the impurities.

The reversing check valve 32 operates in such a manner as to prevent mixture oi the in liowing air and eiiiuent nitrogen. Thus, in the position of the parts shown in Fig. 1, the chamber 40 is at approximately 87 p. s. i. g. while the chamber 30 is approximately at column pressure (7 p. s. i. g.). The column pressure is so much less than the pressure of the inilowing air that the inilowing air easily holds valve 48 on its seat and prevents communication between chambers 38 and 40. Similarly, valve 44 is held on its seat by the diierence in pressure between the inflowing air and the eiiiuent nitrogen, so that there is no communication between chambers 36 and 42.

After the valve I4 is turned through 90, air under pressure is admitted to the chamber 42 and holds valve 48 tight on its seat, thus preventing communication between chambers 42 and 38. At the same time, air ows into chamber 36 by lifting valve 44 oi its seat and the air pressure in chamber 36 serves to hold valve 43 on its seat and prevents communication between chambers 38 and 40.

The method of air separation thus involves cooling the compressed air in the reversing heat exchanger |8 by heat exchange with at least one of the products of rectiiication. the product in this case being the eiliuent waste gases (largely nitrogen). The cooling referred to eiects deposition in the reversing exchanger IB of the impurities, mostly water and carbon dioxide. The passages carrying etiiuent waste gases and inowing air are periodically alternated in order that the eiiluent waste gases may carry of! the accumulated deposits of impurities, thus periodically purging or cleaning out the heat exchanger and preventing the accumulation of dewould otherwise clog the heat exchanger.

The compressed air is further cooled by heat exchange with the same product, namely eiiiuent waste gases (largely nitrogen), this cooling taking place in the heat exchanger 228. The mixture is then passed to the column and is rectlned therein. The rectication of the air in the double column will be well understood by those skilled in the art and need not be detailed here.

A gas rich in the aforesaid one product (nitrogen) is compressed in the compressor ||2, and is cooled in a second heat exchanger |26, |28 by heat exchange with expanded gas. At least a portion oi the thus cooled gas is divided into two streams. Thus, the portion leaving section |34 of unit |28 of the second heat exchanger in conduit |66 is divided, a portion of the gas continuing through the lter |68 on to llqueiler |64 and the remaining portion branching oil by way of conduit |62 to the expansion cylinder |88. Ii' it be assumed for the time being that all the expansion to do external work is accomplished in one cylinder, it will be seen 'that the gas after ex pension leaves the cylinder |38 by way of conduit |15., Thus, one of the aforesaid two streams passes to the expansion engine and is expanded with the performance of external work, while the other portion, namely the portion of gas continuing on in conduit |68 to liquetler |64, is liqueed by heat exchange with expanded gas from the cylinder |38 passing to liqueer |64 by way ofi",

conduits |16 and |18.

Liquid nitrogen passes from liqueer |64 by way of conduit |10 and is expanded substantially isenthalpically through the expansion valve |l`| and passes on to the column by way of the connection 60.

The stream of nitrogen passing into the column by way of connection Bil is mixed liquid and gas. A stream of gaseous nitrogen is withdrawn from the column by way of the connection 62 and passes to the conduit |16 by way of check valve |14, entering the conduit |16 at the intersection |92.

The stream of expansion engine exhaust returns to the compressor inlet |22 by way of the llquefler |64 and the second-named heat exe changer, and the withdrawn stream of gas leaving the column by way of the outlet connection 62 divides and passes into the stream of expansion engine exhaust by way of conduit |18 and passes to heat exchanger I8 by way of conduit |16.

More specifically, in the embodiment of the invention shown in Fig. 1, the secondary circuit nitrogen is expanded isentropically at three levels, namely in the three-stage expansion engine having cylinders |42, |40 and |38. The exhaust from the first stage |42 returns to the compresser inlet by way of a portion of the second heat exchanger |26, |28 and heps to further cool the remaining gas passing to the second and third stages of the expansion engine. The exhaust from the second stage passes through a greater portion of the second heat exchanger If.

and additionally cools the remainder of the gas passing to the third stage. Finally, the engine exhaust from the third stage passes to the liqueer |64 and thus through the second heat exchanger. Secondary circuit nitrogen also supplies additional refrigeration to heat exchanger IB, by Way of liqueer |64, conduit |10, the column, and conduits |12 and |16.

Thus the secondary circuit provides a refrigerant, namely liquid nitrogen and cold gaseous nitrogen, to supply refrigeration to the system which is lost by the fact that oxygen is taken from the system in the liquid form.

Oxygen withdrawn by the opening of valve |00 leaves the line 88 by way of subcooler |04 and is thus subcooled to some extent to minimize loss of oxygen product in storage.

The foregoing description of the operation presumes equilibrium operating conditions. The description of the operation for starting up a warm unit will now be described. To start up and cool a warm unit, the normally closed valves |86 and |90 are kept open, and normally open valve |11 is closed.

Compressed air is supplied by the air compressor 4, and enters the system in the usual manner, passing into the lower column by way of conduit 64 and air inlet 54. The compressed Warm air leaves the column by way of connection 62 and passes through check valve |14 and conduit |12 into the conduit |16, whence it passes through conduit |88 by way of valve |60, which is now open. The compressed air then passes into conduit |80, closing the` check valve |82. Air flows in conduit |80 to passage |98, thus flowing through the unit |20, through conduit 200, unit |26 and conduit 202 to the inlet |22 o1' the nitrogen compressor H2. The nitrogen compressor is now handling air.

Air is compressed in the nitrogen compressor shown.

to approximately 450 p. s. i. g., and passes to the three stages of the expansion engine |36. The expansion in the three cylinders |42, |40 and |38 is substantially the same as during norma1 operation, except that expansion in cylinder |38 takes place over a greater range than during equilibrium operation. With valve |11 closed and valve |86 open, the exhaust of the third cylinder or stage |30 is connected to nearly atmospheric pressure by way of conduits |15 and |113, liqueer |64, conduits |80, |84 (valve |86 being open) and 66, subcooler |04, heat exchanger 226, conduit 223, reversing valve 32, conduit 66, the reversing heat exchanger I8, and out to atmosphere by way of conduit 14, for the position of the valves I4 and 32 shown in Fig. l.

The indicated expansion to a lower pressure (substantially atmospheric) of the third stage |58 of the expansion engine provides ngreater refrigeration than would be provided il the third stage were allowed to expand only to the pressure normally existing during equilibrium operation.

At the same time that air leaves the column by way of secondary circuit outlet connection E2. air also flows into the upper column by way of conduits 16 and 52, through expansion valves S2 and 04 respectively, and out by way of eiiluent line 66.

The` system operates in the manner indicated, quickly cooling down the various luces of Warm apparatus, until liquid begins to accumulate in the column. When liquid begins to accumulate in the column, the composition of the secondary circuit gas changes gradually from substantially air to substantially nitrogen, the compost tion of this secondary circuit gas being ultimately the saine as the composition of the gas above the nitrogen shelf of the lower column. 'lhus the composition of the secondary circuit ges will be substantially 96% nitrogen with about 2i3 of oxygen present.

The operator watches the liquid level in the boiler-condenser in the middle of the double column by means of a liquid level gage, not

When he sees that the liquid has attained a predetermined level (which will be such as to cover the nitrogen coils in the boiler-com denser), he closes valves |99 and |86, and opens valve |11. The apparatus is then in condition for normal operation, although it may take another short time period of from ve to fifteen minutes to get the apparatus in completo condition for the production of oxygen of maximum purity. The normal or equilibrium operation of the apparatus is set forth above.

Reference is now made to Fig. 2 for a descrip` tion of the normal operation of the embodiment of the invention shown therein` Compressed air enters heat exchanger SIS through thc reversing valve 3|4 at substantially 110 F. and 88 p. s. i. g. Air leaves heat exchanger 3|8 by way of reversing check valve 332 and conduit 530 on its way to liqueiler 464 at substantially 250 F. Air leaves liqueiier 464 by way of conduit 354 and goes into the bottom of the column at "215" F'. and 87 p. s. i. g.

Nitrogen eiiluent leaves the column from the connection 353 at approximately -314 F. and 7 D. s, i. g. With the valve 486 closed, the nitrogen goes into liqueer 464 (through passage 505) and leaves liqueer 464 by' way of conduit 5B1 at substantially `-2i'5" F'. The nitrogen eluent passes by Way of reversing' check valve 332 to passage 369 of heat exchanger Sie, entering passage 369 at substantially the aforesaid -275" F..

and leaves exchanger 3|8, discharging to atmosphere at approximately 104 F.

If oxygen product is taken from the apparatus in the liquid form, it may be removed by way of the tap 386 at substantially 290" F. If desired, of course. the oxygen may be pumped to storage under pressure, as shown in the embodiment of Fig. i. If oxygen is taken from the system in the gaseous form, it comes from the column through the vertical stack portion 406 and conduit 509 at 290 F. and 1 p. s. i. g` The oxygen passes through liquener 464 (passage thereof), giving up its refrigeration to the incoming air, and leaving liquener at 262 F. 'I'he oxygen then passes through passage 5|5 of reversing heat exchanger 3|8 and leaves by way of a gaseous oxygen connection 5|1 at 104 F.

Passing now to the secondary circuit of the embodiment shown in Fig. 2, compressed nitrogen enters the heat exchanger 428 at 110 F. and 200 p. s. i. g. Nitrogen leaves heat exchanger 426 by way of conduit 462 at 237 F. and 200 p. s. i. g. During normal or equilibrium operation, valve 41| will preferably be closed, or at most "cracked open. so all or nearly all the nitrogen from heat exchanger 426 passes to the expansion engine, discharging from the expansion engine at 275 F'. and 8'? p. s. i. g. If valve 41| is kept open at all, a small amount (less than 5%) of the secondary circuit nitrogen is liquefied in 464. This liquid expands in valve 41| and goes to the column by way of connection 360 as a gas and liquid mixture.

The expansion engine exhaust passes by way of conduit 416, check valve 483, and conduit 41B to liqueer 484, passing through passage 419 of liqueer 464 and leaving the liquefier at -268 F., and passing at that temperature to the pas sage 496 in heat exchanger 423. The portion of the expansion engine exhaust which passes through liquefier 464 and then through the full length of passage 493 in heat exchanger 426 is approximately 88% of the total expansion engine exhaust. The remainder, approximately 12%, continues on and passes through the cold end of reversing heat exchanger BIB, namely passage 411, leaving the cold end of heat exchanger 318 by way of conduit 496 at 163 F., and going at that temperature into heat ex changer 428 where it joins with the other expansion engine exhaust in passage 498. Nitrogen leaves the exchanger 428 by way of conduit 562 and enters the compressor inlet 422 at 164 F.

Make-up gas, if required, is supplied t0 the secondary circuit by way of connection 362. If the unit is operated with valve 41| closed, such make-up will be only what is needed to replace gas lost through leaks. If valve 41| is open during normal operation, the Weight of gas passing through it must be replaced by an equal weight passing through connection 362.

The method practiced in the apparatus in Fig. 2 thus involves cooling the compressed air in the reversing heat exchanger 3|8 by heat exchange with at least one of the products of rectifcation, that product being the eiilueut waste gases (largely nitrogen) when oxygen is taken from the system as a liquid. When oxygen is taken as a vapor product, the infiowing air is cooled also by the outowing oxygen product.

The cooling referred to effects deposition from the air in the reversing exchanger 3|8 of the impurities, mostly Water and carbon dioxide. The passages carrying eiiluent Waste gases and intlowlng air are periodically alternated in order that the eflluent waste gases may carry off the accumulated deposits of impurities, thus periodically purging out the heat exchanger and pre venting the accumulation of deposits of impurities which would otherwise clog the heat exchanger.

The compressed air is further cooled in lique- Iier 464 by heat exchange with the same product or products depending upon whether oxygen is taken out as a liquid product or a vapor product. Furthermore, however, the inowing air is also cooled in liquefier 464 by a large percentage of the nitrogen exhaust from the expansion engine, this nitrogen being secondary circuit nitrogen. The air mixture leaves liquefer 464 with very little liquid in lt and passes into the column by way oi' conduit 364 and air inlet 354 in the condition of a saturated vapor with a very small percentage by volume of liquid. The percentage of liquid by weight entering the column by way of inlet 354 will normally probably not exceed 6%, so it will be seen by those skilled in the art that the percentage of liquid by volume is almost negligible.

The air is rectified in the double column 350 in a manner which is well understood by those skilled in the art and need not be detailed here.

The gas circulating in the secondary circuit, after normal equilibrium operations have been established, is rich in the nitrogen product; is in fact substantially the same composition as the gas in equilibrium with the liquid on the nitrogen shell of the lower column. This gas may contain as much as 2 of oxygen, and is compressed in compressor 4|2, after which it is cooled in a second heat exchanger 428 by heat exchange with expanded gas returning to the compressor.

The cooled gas leaving heat exchanger 428 passes to the expansion engine 436 Where it expands in doing external work. The thus expanded gas is used to refrigerate the liquefer and also the cold end of the reversing heat exchanger 3|8, as well as cooling the compressed nitrogen from the compressor 4I2. It will be noted that the secondary circuit is at all times connected with the nitrogen shelf of the lower column by way of the secondary circuit column outlet connection 362 and conduit 412. Thus, the secondary system is always ready to be replenished by make-up gas from the nitrogen shelf.

The description of the operation of the embodiment shown in Fig. 2 during the cooldown period will now be discussed. For cooling down the Warm apparatus after a shut-down, normally open valves 382 and 394 are closed, while valves 41| and 486 are opened. 'Compressed air thus enters the system from the air compressor 304, passing through the reversing heat exchanger 318 and into the column by Way of conduit 364 and inlet 354. The compressed air leaves the lower column by way of conduit 362, passing through conduits 412 and 416 to the nitrogen compressor inlet by way of liqueer 464 and heat exchangers 3 I3 and 42B.

The air is compressed in the nitrogen eompressor, is cooled in heat exchanger 428, and. divides; one branch passes to the expansion engine 436 and the other through liqueer 464 to the column by way of the conduit 410, expension valve 41|, and connection 360.

With -by-pass valve 466 open, expansion engine exhaust passes to the effluent line 366 through valve 436, and out to the atmosphere, cooling down exchangers 464 and 3| B. The cooling is 17 regenerative, until ultimately liquid accumulates in the nitrogen shelf immediately below the boiler-condenser in the middle of the column. This liquid overflows and falls to the bottom of the lower column.

As soon as it is observed by the liquid level gage (not shown) that the liquid in the bottom of the column has reached a predetermined level, valves 47| and 486 will be closed, and valves 382 and 394 will be opened, and the apparatus is ready for normal operation, except that it may take up to fifteen minutes of additional operation, while rectification gets started in the upper column, for the apparatus to produce the desired purity of oxygen.

As to both of the embodiments, namely that shown in Fig. 1 and that shown in Fig. 2, it may be pointed out that there is considerable flexibility possible in the operation of the secondary Circuit. The quantity of nitrogen circulated in the secondary circuit can be varied. If the secondary circuit is operated at a low pressure, more nitrogen will be circulated. On the other hand, if the secondary circuit is operated at a higher pressure, it may be operated with the circulation oi" a lesser quantity of nitrogen.

As to the embodiment shown in Fig. 2, it may 'be pointed out that the high pressure of 200 p. s. i. g. for the nitrogen in the secondary circuit is contemplated for the production of liquid oxygen. If gaseous oxygen is produced, the unit may be operated at a lesser high pressure in the secondary circuit-on the order of 160 p. s. i. g.

Further as to the embodiment shown in Fig. 2, it will be understood by those skilled in the art that, during operation with Valve 41| fully closed, ythe member 464 will serve as a liqueer only as to a very small quantity of the entering air. Under such circumstances, member 454 may more properly be termed a third heat exchanger.

While there are in this application specifically described two forms 4which the invention may assume in practice, it will be understood that Ithese forms of the same are shown for purposes of illustration, and that the invention may be 4modified and embodied in various other forms -without departing from its spirit or the scope of the appended claims.

I claim:

1. In a method of separating a gaseous mixture into its components, wherein the compressed gaseous mixture is rectied in a rectification column. the improvement comprising: cooling the compressed gaseous mixture in a rst heat exchanger by heat exchange with at least one of the products of rectification, passing the mixture to the column for rectification therein, compressing a gasV rich in said one product in a compressor, cooling said compressed gas in a second heat exchanger by heat exchange with expanded gas. dividing at least a portion of the thus cooled gas into two streams, passing one of said two streams to an expansion engine, cxpanding said one stream with the performance of external work, liquefying the other of said two streams in a liqueer by heat exchange with oxpanded gas, passing the thus liqueiied stream to the column, dividing the stream of expansion engine exhaust, passing a portion of the exhaust to the compressor by way of the liqueer and the second heat exchanger, passing another portion of the exhaust to the compressor by way of a passage in at least the cold end of the rst heat exchanger, withdrawing a stream of gas in the vapor state from the column, and passing 18 the withdrawn stream of gas into the expansion engine exhaust.

z. In a method of separating a gaseous mixture into its components, wherein the oinpressed gaseous mixture is i'ectined in a rectiiication column, the improvement coiiipiising: cooling the compressed gaseous mixture in a nrs; heat exchanger py heatl exchange with at least one of the products of rectiiication, passing trie mixture to the column ior rectiiication therein, compressing a gas rich in said one product in a compressor, cooling said compressed gas in a second heat exchanger by heat exchange with expanded gas, dividing at least a portion of the thus cooled gas into two streams, passing one or' said two streams to an expansion engine, expanding said one stream with the perioriiiance oi' external work, liqueiying the other or' said two streams in a liqiieiiei by heat exchange with expanded gas, passing the last-named stream to the column, passing the expansion engine exhaust to the compressor by way of the iiquener and the second neat exchanger, withdrawing a stream of gas in the vapor state from the column, dividing said witnorawn stream into at least two portions, separately warming said two portions by heat exchange with separate neat sources, further warming at least a part or said two portions by heat exchange with compressed gas, and finally passing all of the withdrawn stream to the compressor ior compressing as aforesaid.

3. A method as in claim 2, in which one of said portions is warmed before compressing by heat exchange with compressed gaseous mixture.

4. In a method of separating a gaseous mix ture into its components. wherein the coinpressed gaseous mixture is rectiried in a rectification column, the improvement comprising: cooling the compressed gaseous mixture in a iirst heat exchanger by heat exchange with at least one of the products of rectiication, passing the mixture to the column for rectification therein. compressing a gas rich in said one product in a compressor, cooling said compressed gas by heat exchange with expanded gas, dividing the thus cooled gas into two streams, passing one of said two streams to a first expansion engine, expanding said one stream in said rst expansion engine with the performance of external work, warming the thus expanded gas by heat exchange with compressed gas, further cooling the remaining stream of thus cooled gas by further heat exchange with expanded gas, dividing the thus further cooled compressed gas into two streams, passing one of said two streams of further cooled gas to a second expansion engine, expanding said one stream of further cooled gas in the second expansion engine with the performance of external work, warming said stream of further cooled expanded gas by heat exchange with compressed gas, still further cooling the i'emaining stream of further cooled gas by still further heat exchange with expanded gas, dividing the still further cooled gas into two streams, expanding one of said streams of still further cooled gas in a third expansion engine with the periormance of external work, warming the thus expanded stream of still further cooled gas by heat exchange with the remaining stream of still further cooled gas, further warming the still further cooled stream of expanded gas by heat exchange with compressed gas, passing all of the warmed streams of expanded gas back to 19 the compressor, liquefying said remaining stream of still further cooled gas by the aforesaid heat exchange with the stream of expanded gas from the third expansion engine, and using the liquefied stream of gas to provide needed refrigeration in the separation process.

5. Apparatus for separating air into an oxygen product and another product, comprising: a source of air under pressure; a reversng valve; first-named conduit means connecting said source with said valve; at least one reversing heat exchanger having two reversing fluid passages; second-named conduit means connecting the valve with one reversing passage of said heat exchanger; a second reversing valve; thirdnamed conduit means connecting said one reversing passage of the heat exchanger with the second reversing valve; a rectification column having at least an air inlet, two product outlets, and secondary circuit inlet and outlet connections; means, including fourth-named conduit means, to connect the second reversing valve'with the column air inlet; means, including fifth-named conduit means, to connect one of the column product outlets with the second reversing valve; sixthnarned conduit means to connect the second reversing valve with the other one of the reversing passages of the heat exchanger; seventh-named conduit means to connect said other one of the reversing passages of the heat exchanger with the rst-named reversing valve; a product outlet connected to the first-named reversing valve; a secondary circuit compressor having inlet and dist'i''arge connections; a second-named at least one heat exchanger having two uid passages; means, including rst-named secondary circuit conduit means, to connect the discharge connection of the secondary circuit compressor with one passage of the second-named heat exchanger; means to expand an elastic iluid with the performance of external work; means, including second-named secondary circuit conduit means, to connect said one passage of the second-named heat exchanger with the fluid expanding means to supply fluid thereto; a liqueer having two iiuid passages therethrough; means, including third-named secondary circuit conduit means, to connect the second-named secondary circuit conduit means with one passage of the liqueer; a liquid conduit connecting said one passage of the liqueer with said column secondary circuit inlet connection; means to conduct expanded fluid from the duid expanding means to thecompressor inlet connection, said means including the other passage of the liqueer and the other passage of the second-named heat exchanger; means, including fourth-named secondary circuit conduit means, to connect said column secondary circuit outlet connection with said expanded fluid conducting means; and other means to conduct expanded uid from the iiuid expanding means to the compressor inlet connection, said means bypassing the liquefier and including at least a -portion of one passage in the second-named heat exchanger.

6. Apparatus as in claim 5, in which the means to expand an elastic fluid comprises an expansion engine having a plurality of cylinders of which only one exhausts to the liquefier.

'7. Apparatus as in claim 5, in which the means to expand an elastic nuid comprises an expansion engine having a plurality oi cylinders, all of the cylinders being connected to receive fluid at substantially secondary circuit compressor discharge pressure and to exhaust fluid at substantially secondary circuit compressor inlet pressure.

8. Apparatus as in claim '7, in which the several cylinders are connected to expand fluid through different temperature ranges.

9. Apparatus as in claim 5, in which the means to expand an elastic fluid comprises an expansion engine having a plurality of cylinders connected to expand uid through different temperature ranges.

l0. Apparatus for separating air into an oxygen product and another product, comprising: a source oi air under pressure; a reversing valve; rst-named conduit means connecting said source with said valve; at least one reversing heat exchanger having two reversing fluid passages and a third passage, the third passage lying in at least the cold end of the reversing heat exchanger; second-named conduit means connecting the valve with one reversing passage of said heat exchanger; a second reversing valve; thirdnamed conduit means connecting said one reversing passage of the heat exchanger with the second reversing valve; a rectication column having at least an air inlet, two product outlets, and secondary circuit inlet and outlet connections; means, including fourth-named conduit means, to connect the second reversing valve with the column air inlet; means, including fifthnamed conduit means, to connect one of the column product outlets With the second reversing valve; sixth-named conduit means to connect the second reversing valve with the other one of the reversing passages of the heat exchanger; seventh-named conduit means to connect said other one of the reversing passages of the heat exchanger with the rst-named reversing valve; a product outlet connected to the first-named reversing valve; a secondary circuit compressor having inlet and discharge connection; a secondnamed at least one heat exchanger having two iluid passages; means, including first-named secondary circuit conduit means, to connect the discharge connection of the secondary circuit compressor with one passage of the second-named heat exchanger; an expansion engine having intake and exhaust ports; means, including secondnamed secondary circuit conduit means, to connect said one passage of the second-named heat exchanger with the intake port of the expansion engine; a liquener having two fluid passages therethrough; means, including third-named secondary circuit conduit means, to connect the second-named secondary circuit conduit means with one passage of the liqueer; a liquid conduit connecting said one passage of the liquefier with said column secondary circuit inlet connection; means to connect the expansion engine exhaust port with the compressor inlet connection, said means including the other passage of the liqueer and the other passage of the second-named heat exchanger; means, including fourth-named secondary circuit conduit means, to connect the secondary circuit column outlet connection with the last-named means; means to connect the secondary circuit column outlet connection with the third passage of the reversing heat exchanger; and means to connect said third passage with the secondary circuit compressor inlet connection.

11. Apparatus for separating air into an oxygen product and another product, comprising: a source of air under pressure; a reversing valve; first-named conduit means connecting said source with said valve; at least one reversing heat exchanger having two reverslng uid passages and a third passage, the third passage lying in at least the cold end of the reversing heat exchanger; second-named conduit means connecting the valve with one reversing passage of said heat exchanger; a second reversing valve; third-named conduit ineens connecting said one reversing passage of heat exchanger with the second reversing valve; a rectification column having at least an air inlet, two product outlets, and secondary circuit inlet and outlet; connections; means, including fourth-named conduit means, to connect the second reversing valve with the column air inlet; means, including fifth-named conduit means, to connect one of the column product outlets with the second reversing valve; sixth-named conduit means to connect the second reversing valve with the other one of the reversing passages of the heat exchanger; seventh-named conduit means to connect said other one of the reversingr passages of the heat exchanger with the first-named reversing valve; a product outlet connected to the rst-named reversing valve; a secondary circuit compressor having inlet and discharge connections; a second-named at least one heat exchanger having two fluid passages; means, including first-named secondary circuit conduit means, to connect the discharge connection of the secondary circuit compressor with one passage of the seond-named heat exchanger; means to expand an elastic fluid with the performance of external work; means, including second-named secondary circuit conduit means, to connect said one passage of the second-named heat exchanger with the huid expanding means to supply fluid thereto; a liqueer having two fluid passages therethrough; means, including third-named secondary circuit conduit means, to connect the second-named secondary circuit conduit means with one passage of the liqueer; a liquid conduit connecting said one passage of the liqueer with said column secondary circuit inlet connection; means to conduct expanded fluid from the fluid expanding means to the compressor inlet connection, said means including the other passage of the liqueiier and the other passage of the second-named heat exchanger; means, including fourth-named secondary circuit conduit means, to connect said column secondary circuit outlet connection with said expanded fluid conducting means; other means to conduct expanded fluid from the iuid expanding means to the compressor inlet connection, said means by-passing the liqueer and including at least a portion of one passage in the second-named heat exchanger; means to connect the column secondary circuit outlet connection with the third passage of the reversing heat exchanger; and means to connect said third passage with the secondary circuit compressor intake.

12. Apparatus for separating ture into a desired product and waste gases, comprising: a source of compressed gaseous mixture, a reversing heat exchanger, and a rectification column connected in a rectification circuit; a uid compressor, a heat exchanger, fluid expanding means, and a liquelier connected in a refrigeration circuit; means to conduct liquid from the liqueer to the column; and means to conduct fluid from the column to the fluid compressor including a passage inthe reversing heat exchanger.

13. Apparatus as in claim l2, in which the fluid expanding means comprises an expansion engine having a plurality of cylinders of which one is connected to exhaust to the liquefier.

a gaseous mixtu 14. Apparatus as in claim 12, in which the fluid expanding means comprises an expansion engine having a plurality of cylinders, all of the cylinders being connected to receive fluid at substantially fluid compressor discharge pressure and to exhaust fluid at substantially fluid compressor inlet pressure.

15. Apparatus as in claim 12, in which the fluid expanding means comprises an expansion engine having a plurality of cylinders connected to expand fluid through different temperature ranges.

16. Apparatus as in claim 12, in which the lastnamed means includes a conduit connected to conduct expanded fluid from the fluid expanding means to the compressor inlet.

17. Apparatus as in claim 12, in which the lastnamed means also includes a conduit connected to conduct expanded fluid from the fluid expanding means to the compressor inlet, said conduit having two parallel branches, one of which includes a passage in the liqueer and a passage in the second-named heat exchanger, and the other of which includes said passage in the reversing heat exchanger.

18. Apparatus as in claim 17, in which the two branches are joined at their downstream end in the aforesaid passage in the second-named heat exchanger.

19. Apparatus for separating a gaseous mixture into a desired product and waste gases, comprising: a source of compressed gaseous mixture, a reversing heat exchanger having a non-reversing passage through at least the cold end thereof, and a rectication column, connected in a rectification circuit; a riuid compressor, a heat exchanger, uid expanding means, and a liquefier, connected in a refrigeration circuit; means to conduct liquid from the liqueer to the column; and means to conduct fluid from the column to the uid compressor including the non-reversing passage in the reversing heat exchanger.

20. In a method of separating a gaseous mixture into its components, wherein the compressed gaseous mixture is rectified in a rectification column, the improvement comprising: cooling the compressed gaseous mixture in a reversing heat exchanger by heat exchange with at least one of the products of rectification to eiect deposition in the heat exchanger of impurities, periodically alternating the flow of mixture and product to effect removal of the impurities from the heat exchanger, further cooling said mixture by heat exchange with said one product, passing the mixture to the column for rectification therein, compressing a gas rich in said one product in a compressor, cooling said compressed gas in a second heat exchanger by heat exchange with expanded gas, dividing at least a portion of the thus cooled gas into two streams, passing one of said two streams to an expansion engine, expanding said stream of gas with the performance of external Work, liquefying the other of said two streams in a liqueer by heat exchange with expanded gas, passing the liquefied stream of gas to the column, withdrawing a stream of gas in the vapor state from the column, passing the stream of expansion engine exhaust to the compressor by way of means which include the liqueer and the second heat exchanger; dividing said withdrawn stream of gas into at least two streams, and passing the two streams of withdrawn gas into the stream of expansion engine exhaust at different points.

21. A method according to claim 20, in which one of the two withdrawn streams is subjected to heat exchange with the compressed gaseous mixture before passing into the stream of expansion engine exhaust and the other of the two withdrawn streams joins the expansion engine exhaust just prior to passage of said exhaust through the liqueer.

22. In a method of separating a gaseous mixture into its components, wherein the compressed gaseous mixture is rectied in a rectification co1- umn, the improvement comprising: cooling the compressed gaseous mixture in a reversing heat exchanger by heat exchange with at least one of the products of rectification to eiect deposition in the heat exchanger of impurities, periodically alternating the iiow of mixture and product to eiect removal of the impurities from the heat exchanger, further cooling said mixture by heat exchange with said one product, passing the mixture to the column for rectification therein, compressing a gas rich in said one product in a compressor, cooling said compressed gas in a second heat exchanger by heat exchange with expanded gas, passing the thus cooled compressed gas to an expansion engine, expanding the thus cooled compressed gas with the performance of external work, passing the expansion engine exhaust to the compressor in at least two streams, one of which passes to the com- 24 pressor by way of a third heat exchanger and the second heat exchanger in series and the other of which passes to the compressor inlet by way of at least portions of the first heat exchanger and the second heat exchanger in series, withdrawing a stream of make-up gas rich in said one product in the vapor state from the column as needed, and passing the withdrawn stream of make-up gas into the stream of expansion engine exhaust.

SAMUEL C. COLLINS.

References Cited in the iile of thispatent UNITED STATES PATENTS Number Name Date 1,830,157 De Baufre Nov. 3, 1931 1,864,585 De Baufre June 28, 1932 2,091,349 Bergman Aug. 31, 1937 2,417,279 Van Nuys Mar. 1l, 1947 2,424,201 Van Nuys July 15, 1947 2,460,859 Trumpler Feb. 1949 2,470,483 Gadwa May l'7, 1949 2,482,303 Van Nuys Sept. 2D, 1949 2,496,380 Crawford Feb. 'i'. 1950 2,530,602 Dennis Nov. 21, 1950 FOREIGN PATENTS Number Country Date 468,212 Canada Sept. 19, 1950 

